Many forms of heat pump-type residential heating systems have been devised. These systems normally include a refrigerant fluid compressor that is interconnected with two heat exchanger units. These two heat exchanger units are alternatively operated as evaporators or condensers depending upon the positioning of a directional control valve in the interconnecting refrigerant fluid conduit. The one heat exchanger unit is normally positioned within the interior of a residential building and is associated with heating or cooling apparatus, such as the well-known fan and coil type. The other heat exchanger unit is located exteriorily of the building and the heat pump is operated to either add heat to the interior of the residence or to remove heat and permit it to be merely dissipated at the exterior of the building.
While the heat pump system is inherently an efficient heating and cooling system for residences, there is nevertheless some loss of heat during the operation of such apparatus. Attempts have been made to improve the economy of the operation by utilizing excess heat that is developed within the system for other purposes. Primarily, this excess heat is attempted to be utilized in performance of auxiliary heating functions and specifically, in the heating of water that is also used within a residential household. An example of such a previously devised system is disclosed in U.S. Pat. No. 3,916,638, granted Nov. 4, 1975 to A. Carl Schmidt. The system disclosed in that patent includes a compressor, two heat exchanger units and a water heater also having a heat exchanger unit. The interconnection of the several units, however, is such that the heat exchanger of the water heater is only selectively interconnectable to the system in one mode of operation. Effectively, the water heater can only be functioning when the system is operated in the cooling mode. With the interconnection of the heat exchanger for the water heater as shown in that patent, the patented system will be ineffective in attempting to obtain sufficient heat with which to operate the water heater when the system is operated in a heating mode.